I play a bunch of games where I just really want a mouse and the touchpads make that feel relatively natural in a way that joysticks just don't.
I do agree, though - the focus on the touchpads on the original steam controller was perhaps over the top, and the absence of a second stick was limiting. I think the deck gets it right: You have two of each, one for each hand.
I can play games designed for controllers, and I can play games designed for mice, and everything just works.
If I'm playing a game designed around a console experience, I want the sticks - they feel natural in that space in a way that the touchpads don't compare with.
If I'm playing a game designed for a mouse and keyboard... I definitely don't want the sticks. I want the touchpads (at least one of them). The sticks feel horrible as a mouse for these games (although sometimes one can replace WASD panning controls)
Basically - games like Rimworld/Dwarf Fortress DO NOT WORK without the touchpads. Period. The touchpads are not "alternative"... the touchpads are the reason the deck can make those games playable.
You could get mouse-level accuracy with a gamepad with a bit of practice.
The mouse and trackpad emulation of the steam controller makes it one of the best ways to control a media PC though.
[0]https://www.printables.com/model/259733-steam-deck-grip-exte...
Edit: I guess it also help that while I've played Stellaris extensively on a desktop, I never played ONI outside of the deck, so I don't know what I'm missing.